Barth syndrome (BTHS) is a severe, X-linked disorder resulting from mutations in the tafazzin gene. It is characterized by dilated cardiomyopathy, skeletal myopathy, neutropenia, growth retardation, abnormal mitochondria, and a high rate of cardiac arrythmia. BTHS cells exhibit decreased levels of the phospholipid cardiolipin (CL) and aberrant CL acyl species. Consistent with this, tafazzin is a transacylase that catalyzes the remodeling of CL (replacing existing fatty acids on CL with new ones). While all BTHS patients have aberrant CL composition, the clinical presentation of BTHS is highly variable, even among patients with the same tafazzin mutation. This indicates that the outcome of defective tafazzin is strongly influenced by physiological modifiers. The current gap in our understanding of the function of tafazzin and the identity of the modifying factors complicates the treatment of BTHS. The long-term goal of the proposed research is to elucidate the cellular role and physiological modifiers of tafazzin. To this end, an innovative genetic approach will be implemented to identify synthetic lethal interactions with tafazzin. The identification of synthetic lethals, i.e., genes that are essential for survival in the absence of the gene of interest, is a powerful method to assign function to a gene and to identify factors that exacerbate its loss. In the proposed study, synthetic lethals will first be identified in the well-characterized yeast model for BTHS (the taz1? mutant), and synthetic lethality will then be tested in mammalian cardiomyocytes. This study will test the hypothesis that loss of tafazzin is synthetically lethal with mutants in pathways that require CL. The specific aims are as follows: 1) A genome-wide screen of all (4,815) viable yeast deletion mutants will be carried out to identify all mutants that are synthetically lethal with the yeast taz1? mutant. 2) The synthetic lethal interactions discovered in yeast will be tested in mammalian cardiomyocytes, using RNAi methodology to knock down expression of tafazzin and potential interacting genes. The successful identification of synthetic lethal interactions with tafazzin will provide new insights into the pathology and treatment of BTHS. This knowledge will lead to the identification of general mechanisms underlying dilated cardiomyopathy and other CL-associated disorders of mitochondrial dysfunction. PUBLIC HEALTH RELEVANCE The proposed study will identify modifying physiological factors that affect the severity of Barth syndrome, a disorder of mitochondrial lipid metabolism that causes heart failure and sudden death due to dilated cardiomyopathy and cardiac arrhythmia. The identification of these modifying factors will lead to new rationales for the treatment of Barth syndrome. Furthermore, this knowledge will help to elucidate mechanisms underlying the pathology of cardiomyopathy and cardiac arrhythmia, and will also have implications for other conditions associated with mitochondrial lipid metabolism, including ischemia, aging, Parkinson's disease, and diabetes.